Drosophila melanogasterlarvae were pre–stimulated with high concentrations of six homologous alcohols (C4–C9) and then tested for adaptation and cross–adaptation using these same alcohols, four aliphatic n–acetates and three acids. Pre–stimulation with hexanol effectively reduced to zero (abolished) test responses to all six alcohols, whereas test responses to hexanol were only affected by pre–stimulation with hexanol. This substance appears to play a fundamental role in the organization of the larval olfactory system. Test responses to butanol and pentanol, and the effect of pre–stimulation with butanol and pentanol, were not significantly different, indicating that they are sensory equivalents. Heptanol, octanol and nonanol induce a complex set of responses among one another. Cross–adaptation between functional groups was observed, in particular following pre–stimulation with hexanol, but there was also evidence that functional groups are coded separately. A model of olfactory processing in the fruitfly maggot is presented that explains the data and provides predictions for future anatomical, genetic and electrophysiological studies.